Lighting equipment using LED elements has come into wide use. Here, if it is desired to shorten the design lead time for lighting equipment such as desk lamps and other lighting lamps, it is recommended to modularize light source units. For example, FIG. 2 in patent document 1 shows an LED module constructed by mounting a plurality of LED chips (LED elements) and a lighting circuit on the same substrate.
FIG. 7 is a diagram redrawn from FIG. 2 given in patent document 1, showing a cross-sectional view of an LED lamp that uses a lamp base (GX53 type) conforming to the IEC standard.
The LED module shown in FIG. 7 comprises a circuit substrate 2, a driver circuit 4 (lighting circuit), and LEDs 3 (LED elements). The driver circuit 4 is mounted on the upper surface of the circuit substrate 2, while the LEDs 3 are mounted on the lower surface of the circuit substrate 2. The LED module shown in FIG. 7 is fitted into the housing of a lamp base 1, and is held in place by means of a lamp cover case 5. If it is desired to reduce the thickness of the module, the LEDs 3 should be mounted using a technology known as COB (Chip on Board). COB is a technology that mounts LED elements in bare chip form (hereinafter called the LED dies unless specifically designated otherwise) directly on the circuit substrate 2.
When mounting the LED dies using the COB technology, at least the area where the LED dies are mounted on the surface of the circuit substrate must be made to have a high reflectance. For example, in FIG. 3 given in patent document 2, there is shown a light-emitting module 1a (LED module) in which the LED die mounting area on the surface of the circuit substrate is made to have a high reflectance.
FIG. 8 is a diagram redrawn from FIG. 3 given in patent document 2, showing a plan view of the light-emitting module 1a as viewed from the light-emitting side thereof (hereinafter called the upper surface side).
No electronic components other than the light-emitting elements 21 (LED dies) are mounted on the module substrate 5b (circuit substrate) of the light-emitting module 1a. Further, the light-emitting module 1a has a COB-type structure. A reflective layer 11, a positive electrode power feed conductor 12, and a negative electrode power feed conductor 13 are formed on the upper surface of the module substrate 5b. The plurality of light-emitting elements 21 (LED dies) are arranged in the form of an array on the surface of the reflective layer 11, and the plurality of light-emitting elements 21 are connected in series on a row-by-row basis by bonding wires 23. The light-emitting elements 21 in each row are supplied with power via edge bonding wires 24. A sealing hole 25a formed in a frame member 25 is filled with a sealing member 28. The module substrate 5b has a structure in which a thin insulating layer is formed on the surface of a metal base plate such as aluminum for enhanced heat dissipation.
The reflective layer 11 and the power feed conductors 12 and 13 are patterned on the surface of the insulating layer 7 of the module substrate 5b by plating and etching. The power feed conductors 12 and 13 are formed in such a manner as to sandwich the reflective layer 11 from both sides thereof. The upper surfaces of the reflective layer 11 and power feed conductors 12 and 13 are formed from Ag to provide a higher reflectance than that of the insulating layer (not shown) formed on the surface of the module substrate 5a. The total reflectance of each of the reflective layer 11 and power feed conductors 12 and 13 is about 90.0%. Two power feed terminals 14 and 15 are also patterned on the surface of the insulating layer, and the light-emitting module 1a is connected to a lighting apparatus via insulating coated wires not shown. The reflective layer 11 also serves as a heat spreader which spreads out the heat generated by the plurality of light-emitting elements 21.